Using the Basic Components › Using Existing Tape Data Sets

Using Existing Tape Data Sets

When allocation processing occurs at the operating system tape selection exit (Subsystem Interface 78) for an existing data set residing on a CA Vtape Virtual Volume, all devices except the CA Vtape Virtual Devices are marked ineligible in the Eligible Device List (EDL).

Note: The esoteric or generic specified in the UNIT JCL parameter or in the device type field of the data set catalog entry must contain Virtual Device addresses. If not, CA Vtape will not be able to intercept the mount request.

SRM selects the actual device from this list and requests a mount for a specific Virtual Volume on the selected Virtual Device. The Virtual Device Engine initiates the allocation process by checking where the Virtual Volume resides. If it is found in the DASD buffer, it is mounted. If not, the Virtual Device Engine sends a request to the Backstore Engine to start the Recall process from a Backstore tape.

To locate the appropriate Backstore tape, the Backstore Engine searches the ICF catalog for the standard name used for Externalized Virtual Volumes. The standard name is prefix.VVE.Vvolser.type, where prefix is the DSN prefix defined for CA Vtape use, volser is the required Virtual Volume, and type can be PRIMARY or DUPLEX. If no entry is found, an EOV is written to the cache LDS and the mount is completed.

Note: A PRIMARY Backstore tape will be selected by default. A DUPLEX tape will be automatically requested when cataloged if a PRIMARY tape is not cataloged. You can change the selection order in the Backstore Engine by issuing the SET RECALL console command. For more information about the SET RECALL console command, see the chapter “Console Commands.”

Note: If the USS Backstore feature is active, the mounted file systems are also used as recall sources. The SET RECALL console command can be used for these recall sources also.

After the ICF catalog entry is found, the corresponding Backstore tape is mounted and positioned to the requested physical block. After the Virtual Volume is opened and the Recall process has begun, the Virtual Volume mount request is satisfied and data begins passing to the Virtual Device and the application.

Note: The Virtual Volume mount is delayed until the Virtual Volume is fully restored to the DASD buffer if the subsystem the Virtual Device belongs to is configured as a Recall client.